An optical imaging device (e.g. a video camera, a digital camera, etc.) is typically equipped with a lens. In order to control the amount of light incident on the light sensitive surface inside the optical imaging device via the lens, an iris is mounted inside the lens. The extent to which the iris is opened or closed corresponds to a different amount of incoming light. In the existing optical imaging device, the extent to which the iris is opened or closed is determined by a control voltage provided from the imaging device to the iris.
For example, when in operation, the video camera calculates the brightness of each frame of image and compares the brightness with a target brightness value having been set to obtain a relative brightness value. The relative brightness value, which may be in the form of a ratio in dB, represents a difference between the current brightness level (Video level) and the target brightness value. Then, the control voltage of the iris is adjusted in real time according to an iris control model stored in advance in a storage unit of the video camera, so as to change the amount of incoming light of the iris. The so-called iris control model, as illustrated in FIG. 1, may be a functional relationship between iris control voltage offsets and relative brightness values, which functional relationship is derived from the characteristics of the iris. When the relative brightness value is changed, the video camera can determine an iris control voltage offset from the iris control model, thus to adjust the iris control voltage to make the relative brightness value to be 0, i.e. back to the origin (a convergence target) of FIG. 1.
In another example, U.S. Pat. No. 5,739,854 discloses an apparatus being capable of adjusting in real time the amount of incoming light. In this apparatus, a detection unit is arranged to detect in real time the extent to which the iris is opened or closed, and to transport detected information to a circuit control unit; the circuit control unit performs certain processing for the information, and further transfers the processing result to an iris control unit; and the iris control unit adjusts the extent to which the iris is opened or closed according to an instruction of the circuit control unit. When there are multiple irises, a synchronization component is further arranged in the apparatus to synchronize control signals that are outputted from the iris control unit.
However, the iris control model stored in advance in the existing optical imaging device is set with respect to specific lens of the original manufacturer. In fact, lenses produced by different manufacturers may be different, and characteristics of their irises may also be different. Thus, the optical imaging device fails to be adaptive to those lenses of different categories, and is greatly limited in usage. For example, when a lens is replaced by that of a different category or that from a different manufacturer, due to the mismatch of the iris with the iris control model preset in the storage unit, a phenomenon that different irises respond at different rates to the same control voltage may occur, thus a problem of iris hunting may arise.
Furthermore, in the case that the curve of the iris control model is too steep, i.e. the control voltage offset corresponding to the relative brightness value is too large, the control voltage may also be large, thus the iris may be caused to act too fast. When the speed at which the iris acts exceeds the range that can be controlled by the optical imaging device, fast iris hunting may occur. As illustrated in FIG. 2, when fast iris hunting occurs, for the reason that the iris is opened or closed variably, the current brightness level (Video Level) may vary significantly with time.
In the existing optical imaging device, there are similar problems in controlling other elements or performances of the lens, thus leading to limited categories of lenses being suitable to be mounted in the optical imaging device.